New commercial products are becoming available which provide special advantage because of fine particle size. Zinc oxide is widely utilized as an ingredient in human health products. Superior results are now obtained by the use of submicron transparent zinc oxide powder. The ultrafine zinc oxide provides advantage of UVA/B-protection in cosmetic formulations, and exhibits enhanced antimicrobial capacity and functions as a preservative.
Alkali metal bicarbonate is another commodity reagent which has found application in a broad variety of products such as laundry detergents, deodorizers, creams and lotions, dentifrices, antacids, buffers, fungicides, and the like.
There is evidence that fine particle size alkali metal bicarbonate or ammonium bicarbonate can exhibit increased reactivity in comparison with coarse grain bicarbonate salts. In soda cracker production, finely divided sodium bicarbonate ingredient is more efficiently distributed and effectively reactive during the cracker dough preparation. The finished baked cracker is an improved product which has a substantially uniform texture, flavor and surface color, and a consistent pH throughout.
The inclusion of particulate alkali metal bicarbonate in an antiperspirant-deodorant cosmetic stick provides a product with improved deodorant properties. However, coarse grain alkali metal bicarbonate has an undesirable tendency to settle in an antiperspirant-deodorant cosmetic stick matrix. The use of ultrafine alkali metal bicarbonate as a deodorant ingredient in cosmetic stick and roll-on type personal care products is being investigated, since the ultrafine particles have less tendency to settle than coarse grain particles when dispersed in a liquid or semi-solid matrix.
A limiting factor has been the unavailability of alkali metal bicarbonate or ammonium bicarbonate powder which is composed of free-flowing ultrafine particles that are not in an agglomerated state.
Dimensional instability of a cosmetic stick product containing bicarbonate ingredient, and the esthetic appearance and the "feel" on the skin, are additional difficulties encountered in the preparation of a low residue antiperspirant-deodorant cosmetic product. The high density of a suspended particle-phase of bicarbonate ingredient relative to the low density of an organic matrix phase contributes to the instability and settling of the bicarbonate particle phase in a cosmetic stick or roll-on personal care product.
In addition, a bicarbonate ingredient often is incompatible with the active astringent salts and with other ingredients of conventional cosmetic stick products. A bicarbonate ingredient in direct contact with acidic ingredients is susceptible to decomposition into carbon dioxide and water.
There is continuing interest in the development of reagents such as alkali metal bicarbonate and ammonium bicarbonate which have an ultrafine particle size, and exhibit a novel combination of properties when utilized as an ingredient in personal care, biologically active, household, and specialty type products. There is also interest in the development of a bicarbonate powder which is in a form that is stable when blended with an acidic ingredient in a formulation.
It is an object of this invention to provide an alkali metal bicarbonate or ammonium bicarbonate powder which has an ultrafine particle size, and which is free-flowing and essentially free of agglomerated solids.
It is a further object of this invention to provide a process for producing an ultrafine bicarbonate salt powder composition which is a co-micronized blend of crystalline compounds composed of discrete particles which are coated with a polymer.
Other objects and advantages of the present invention shall become apparent from the accompanying description and examples.